MRI coil and MRI apparatus

ABSTRACT

In order to mitigate the feeling of confinement experienced by a subject (patient) and improve the S/N ratio of an MRI coil when used as a head coil, there is provided an MRI coil  10  comprising a pair of opposing coils  1  and  2  whose coil surfaces face each other with an imaging space interposed, and a quadrature coil  3  which has a coil surface orthogonal to the coil surfaces of the opposing coils  1  and  2  and surrounds the imaging space. When the MRI coil  10  is used as a head coil, the quadrature coil  3  is fitted over the eyes of a subject H, and the opposing coils  1  and  2  are positioned near the ears of the subject H.

RELATED APPLICATION

This is a division of Ser. No. 09/289,907 filed Apr. 13, 1999 now U.S.Pat. No. 6,241,669 issued on Jun. 5, 2001.

BACKGROUND OF THE INVENTION

The present invention relates to an MRI (magnetic resonance imaging)coil, and more particularly, to an MRI coil capable of mitigatingfeeling of confinement experienced by a subject (patient) and improvingthe S/N ratio when used as a head coil.

An example of a conventional MRI head coil is shown in FIG. 1.

The MRI head coil 70 has a cylindrical shape containing an imaging spacetherein for accommodating the head of a subject H.

The conventional MRI head coil 70 has the following problems:

(1) Since the coil has a cylindrical shape enveloping the head of thesubject H and has few opening portions, visual and auditory perceptionof the subject H is extensively restricted and the subject's exhaledbreath fills the coil, giving the subject H a confined feeling.

(2) Since the coil envelops the head of the subject H, the coil requiresa cavity having a greater size than the distance from the tip of thenose to the back of the head, and the coil therefore cannot besignificantly reduced in size. Thus, because the distance between thesubject H and the coil cannot be reduced, the S/N ratio is lowered.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an MRI coil capableof mitigating the confined feeling experienced by a subject (patient)and improving the S/N ratio when used as a head coil.

In accordance with a first aspect of the present invention, there isprovided an MRI coil comprising a pair of opposing coils whose coilsurfaces face each other with an imaging space interposed, and aquadrature coil which has a coil surface orthogonal to the coil surfacesof the opposing coils and surrounds the imaging space.

When the MRI coil of the first aspect is used as a head coil, thequadrature coil is fitted over the head of the subject, and the opposingcoils are positioned near the ears of the subject. In this condition,the quadrature coil overhangs the eyes of the subject, but does notcover the head top, nose or mouth. The opposing coils are placed nearthe ears of the subject, but do not completely cover the ears. Moreover,the exhaled breath of the subject does not fill the coil. Hence, thecoil does not give the subject a confined feeling. Furthermore, sincethe quadrature coil does not cover the nose, the coil does not require acavity having a greater size than the distance from the tip of the noseto the back of the subject H's head, and the coil can be reduced insize. The reduced size shortens the distance between the subject and thecoil, thereby improving the S/N ratio.

In accordance with a second aspect of the present invention, there isprovided the MRI coil as described regarding the first aspect, whereinthe opposing coils and the quadrature coil are integrally combined sothat their positions relative to one another are maintained unchanged,and part of the coil surfaces of the opposing coils are opened outward.

A coil is preferably disposed as close to the subject as possible inorder to improve the S/N ratio, Accordingly, the spacing between theopposing coils is made slightly greater than the size of the subject.However, this may result in difficulties in fitting the coil over thehead of the subject when the coil is used as a head coil. The MRI coilof the second aspect has part of the coil surfaces of the opposing coilsopened outward, facilitating fitting of the coil over the head of thesubject. Moreover, since the opposing coils and the quadrature coil areintegrally combined so that their relative positions remain unchanged,the coil requires no pivotal attachment mechanism, thereby simplifyingthe structure.

In accordance with a third aspect of the, present invention, there isprovided the MRI coil as described regarding the first aspect, whereinthe opposing coils are pivotally attached to the quadrature coil, andthe pair of opposing coils is allowed to be opened in an inverted V-likeshape.

A coil is preferably disposed as close to the subject as possible inorder to improve the S/N ratio. Accordingly, the spacing between theopposing coils is made slightly greater than the size of the subject.However, this may result in difficulties in fitting the coil over thehead of the subject when the coil is used as a head coil. The MRI coilof the third aspect has the pair of opposing coils that is allowed to beopened in an inverted V-like shape, facilitating fitting of the coilover the head of the subject. Moreover, this eliminates the need to formpart of the opposing coils in an opened shape, thereby simplifying theshape of the opposing coils.

The MRI coil of the present invention may be used as, for example, aknee coil for imaging the knee.

In accordance with a fourth aspect of the present invention, there isprovided an MRI apparatus comprising static magnetic field generatingmeans for generating a static magnetic field to be applied to a subjectduring image capture, wherein the MRI coil as described regarding any ofthe first through third aspects is employed to acquire NMR signals fromthe subject.

The MRI coil and MRI apparatus of the present invention can thusmitigate feeling of confinement experienced by a subject (patient) andimprove the S/N ratio when the coil is used as a head coil.

Further objects and advantages of the present invention will be apparentfrom the following description of the preferred embodiments of theinvention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a conventional MRI head coil.

FIGS. 2A-2C are views taken from three orthogonal directions of an MRIhead coil in accordance with the first embodiment of the presentinvention.

FIG. 3 illustrates the MRI head coil of FIG. 2 prior to being fittedover a subject.

FIG. 4 illustrates the MRI head coil of FIG. 2 fitted over the subject.

FIGS. 5A-5C are perspective news of an MRI head coil in accordance withthe second embodiment of the present invention.

FIG. 6 illustrates the configuration of a vertical magnet MRI apparatusin accordance with the third embodiment of the present invention.

FIG. 7 illustrates imaging of the head in the vertical magnet MRIapparatus of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in more detail withreference to its embodiments shown in the accompanying drawings.

First Embodiment

FIGS. 2A-2C are respectively a front elevational view, a right side viewand a plan view of an MRI head coil in accordance with the firstembodiment of the present invention.

The MRI head coil 10 comprises a pair of opposing coils 1 and 2 whosecoil surfaces face each other with an imaging space interposed, and aquadrature coil 3 which has a coil surface orthogonal to the coilsurfaces of the opposing coils 1 and 2 and surrounds the imaging space.

The opposing coils 1 and 2 have a generally circularly annular shape asa whole, except that their respective front peripheral portions 1 a and2 a are opened outward.

The quadrature coil 3 has a generally track-like annular shape (i.e., anannular shape consisting of semicircles and straight lines like a racetrack for field sports).

The opposing coils 1 and 2 and the quadrature coil 3 are integrallycombined so that their relative positions are maintained unchanged.

FIG. 3 illustrates the MRI head coil 10 being fitted over the head of asubject.

A cradle C is provided with a head rest R for supporting the head of thesubject H a certain distance above the cradle C, and a concave portion Kfor inserting the MFRI head coil 10 below the head rest R. The MRI headcoil 10 is set behind the head of the subject H.

First, the subject H is laid on the cradle C at a position such that thehead of the subject H is supported by the head rest R.

The MRI head coil 10 is then slid to be fitted over the head of thesubject H. That is, the MRI head coil 10 is slid to a position at whichthe quadrature coil 3 overhangs the eyes of the subject H.

FIG. 4 is a cross sectional view illustrating the MRI head coil 10fitted over the head of the subject H.

The opposing coils 1 and 2 are electrically connected so that theircurrents flow in the same direction (the connection may be either serialor parallel), to constitute so-called Helmholtz coils. This generates ahomogeneous magnetic field in the imaging space between the opposingcoils 1 and 2.

The quadrature coil 3 is “quadrature connected” with respect to theopposing coils 1 and 2. This achieves effective reception of NMRsignals.

The above-described MRI head coil 10 offers the following advantages:

(1) The quadrature coil 3 overhangs the eyes of the subject H, but doesnot cover the head top, nose or mouth. The opposing coils 1 and 2 areplaced near the ears of the subject H, but do not completely cover theears. Moreover, the exhaled breath of the subject H does not fill thecoil. Hence, the coil does not give the subject H a confined feeling.

(2) Since the quadrature coil 3 does not cover the nose, the coil doesnot require a cavity having a greater size than the distance from thetip of the nose to the back of the subject H's head, and the coil may bereduced in size. The reduced size shortens the distance between thesubject H and the coil, thereby improving the S/N ratio.

(3) Since the front peripheral portions 1 a and 2 a of the opposingcoils 1 and 2 are opened outward, the coil is easy to fit over the headof the subject H.

(4) Since the opposing coils 1 and 2 and the quadrature coil 3 areintegrally combined so that their relative positions are maintainedunchanged, the coil requires no pivotal attachment mechanism, therebysimplifying the structure.

Second Embodiment

FIG. 5A is a perspective view of coils in an MRI head coil in accordancewith the second embodiment of the present invention.

The MRI head coil 20 comprises a pair of opposing coils 4 and 5 whosecoil surfaces face each other with an imaging space interposed, and aquadrature coil 6 which has a coil surface orthogonal to the coilsurfaces of the opposing coils 4 and 5 and surrounds the imaging space.

The opposing coils 4 and 5 have a generally circularly annular shape.

The quadrature coil 6 has a generally track-like annular shape.

The opposing coils 4 and 5 and the quadrature coil 6 are integrallycombined by means of covers 14-16 as will be described hereinafter.

FIG. 5B is a perspective view of the covers for the MRI head coil 20.

The opposing coil 4 is contained in a left cover 14. The opposing coil 5is contained in a right cover 15. The quadrature coil 6 is contained ina central cover 16.

The left and right covers 14 and 15 are pivotally attached to thecentral cover via hinges, and are allowed to be opened in an invertedV-like shape. That is, the opposing coils 4 and 5 are allowed to beopened in an inverted V-like shape.

FIG. 5C is a perspective view of the MRI head coil 20 with its covers 14and 15 opened.

While the opposing coils 4 and 5 shown in FIG. 5C are opened in aninverted V-like shape in the horizontal direction, the opposing coilscan instead be configured to be opened in a V-like shape in the upwardor downward direction.

The above-described MRI head coil 20 offers the following advantages:

(1) Since the coil has a large opening portion, the coil intercepts onlya small portion of the field of view of the subject H and is not filledwith the exhaled breath of the subject H, thereby giving the subject Hno feeling of confinement.

(2) Since the quadrature coil 6 does not cover the nose, the coil doesnot require a cavity having a greater size than the distance from thetip of the nose to the back of the subject H's head, and the coil can bereduced in size. The reduced size shortens the distance between thesubject H and the coil, thereby improving the S/N ratio.

(3) Since the opposing coils 4 and 5 are opened in an inverted V-likeshape, the coil is easy to fit over the head of the subject H.

(4) The opposing coils 4 and 5 can have a simple shape.

Third Embodiment

FIG. 6 illustrates the configuration of a vertical magnet MRI apparatusemploying the MRI head coil of the present invention.

The vertical magnet MRI apparatus 100 comprises a vertical magnetapparatus 30, a movable chair 40 and a movable table (not shown).

The vertical magnet apparatus 30 has a vertical opposing magnet 31 whoseopposing surface is vertically disposed, another vertical opposingmagnet 32 (not shown) which is disposed opposite to the magnet 31, arail 33 (34) provided on the opposing surface of the vertical opposingmagnet 31 (32), a table stopper apparatus (not shown) and a chairstopper apparatus 35.

The rail 33 (34) is provided for supporting the cradle coming out of themovable table.

The table stopper apparatus and the chair stopper apparatus 35 areprovided with connectors for establishing electrical connection with themovable table or the movable chair 40.

The movable chair 40 has a supporting panel 41 for supporting the MRIhead coil 10 slidably in the vertical direction.

In Imaging operation, the subject H Is seated on the movable chair 40with the movable chair 40 drawn out of the vertical magnet apparatus 30as shown in FIG. 6. At this time, the MRI head coil 10 is raised. Thenthe MRI head coil 10 is lowered to be fitted over the head of thesubject H. Subsequently the movable chair 40 is moved into the spacebetween the opposing surfaces of the vertical magnet apparatus 30 asshown in FIG. 7. Thereafter, the imaging is performed.

The above-described vertical magnet MRI apparatus 100 allows imaging ofthe head to be easily done with a subject seated on a chair.

Many widely different embodiments of the invention may be configuredwithout departing from the spirit and the scope of the presentinvention. It should be understood that the present invention is notlimited to the specific embodiments described in the specification,except as defined in the appended claims.

What is claimed is:
 1. A magnetic resonance imaging coil for use on ahead of a subject being disgnosed, said imaging coil consisting of: apair of similar coils pivotally and movably disposed substantiallyparallel to and opposite each other, and having coil surfaces generallyfacing each other with an imaging space interposed there-betweeen and inwhich said imaging space said head is positioned for diagnosis, each ofsaid pair of similar coils having a closed circular shape and pivotallymovable to form an opening therebetween which is larger than thedistance between said pair of similar coils in a parallel state; and anorthogonal coil having a coil surface which is disposed to be orthogonalto said coil surfaces of said pair of similar coils and surrounding saidimaging space, said pair of similar coils being pivotally attached tosaid orthogonal coil; wherein a combination of said two similar coilsand said orthogonal coil is positioned for imaging by fitting saidcombination about a top of said head through said opening created bypivotally moving said oppositely positioned pair of similar coils sothat said head is placed in said imaging space with said pair of similarcoils fitted on the sides of said head where ears thereof are located,and said orthogonal coil is fitted over a face of said head andoverhanging eyes of said head without covering the head top, nose ormouth, and so that said pair of similar coils are placed near and onlypartially covering said ears of said head, whereby the entire structureof said imaging coil is reduced in size to thereby improve signal tonoise ratio, and whereby the entire structure is easy to fit over saidhead and does not cause a claustophobic reaction of the subject beingimaged.
 2. The coil of claim 1, wherein said pair of similar coils andsaid orthogonal coil are integrally combined so that relative positiontherebetween is movable.
 3. The coil of claim 1, wherein said pair ofsimilar coils are positioned so that in a pivotally moved state, saidpair of similar coils form a V with opening of said V being away fromsaid orthogonal coil in a horizontal direction.
 4. The coil of claim 1,wherein each of said pair of similar coils is covered with a covering.5. The coil of claim 4, wherein said orthogonal coil is covered with acovering.
 6. The coil of claim 1, wherein said orthogonal coil comprisesa circular annular shape.
 7. A magnetic resonance imaging apparatuscomprising: means for generating a static magnetic field; means forapplying said static magnetic field to a head of a subject during imagecapture; and a magnetic imaging coil for use on said head, said imagingcoil consisting of: a pair of similar coils pivotally and movablydisposed substantially parallel to and opposite each other, and havingcoil surfaces generally facing each other with an imaging spaceinterposed there-between and in which said imaging space said head ispositioned for diagnosis, each of said pair of similar coils having aclosed circular shape and pivotally movable to form an openingtherebetween which is larger than the distance between said pair ofsimilar coils in a parallel state; and an orthogonal coil having a coilsurface which is disposed to be orthogonal to said coil surfaces of saidpair of similar coils and surrounding said imaging space, said pair ofsimilar coils being pivotally attached to said orthogonal coil; whereina combination of said two similar coils and said orthogonal coil ispositioned for imaging by fitting said combination about a top of saidhead through said opening created by pivotally moving said oppositelypositioned pair of similar coils so that said head is placed in saidimaging space with said pair of similar coils fitted on the sides ofsaid head where ears thereof are located, and said orthogonal coil isfitted over a face of said head and overhanging eyes of said headwithout covering the head top, nose or mouth, and so that said pair ofsimilar coils are placed near and only partially covering said ears ofsaid head, whereby the entire structure of said imaging coil is reducedin size to thereby improve signal to noise ratio and whereby the entirestructure is easy to fit over said head and does not cause aclaustophobic reaction of the subject being imaged.